This invention relates to an improved auxiliary combustion chamber for an internal combustion engine, the inner surface of which is a ceramic.
In the case where the auxiliary combustion chamber of an internal combustion engine is made of a ceramic material surrounded by a metal member, it is desirable that the inner chamber portion be made of a ceramic material that is excellent in heat insulation in order to improve its heat efficiency. However, if the chamber portion is made of a ceramic high in heat efficiency, then the temperature gradient betwen the inner and outer walls thereof is large. This is especially true when a ceramic having a high thermal expansion coefficient is used and a considerably large tensile stress is induced in the outer wall which can be sufficient to break the chamber. Therefore, it is effective to apply an initial compressive stress to the ceramic component, thereby to suppress the tension due to thermal stress. For this purpose, shrinkage fit of a ceramic liner within a metal member or casting the metal around the liner may be employed. Since the ceramic chamber liner is partially spherical, it is impossible to employ the shrinkage fit method, and the casting method is generally employed.
This is especially the case where the chamber liner is made of sintered, partially stabilized zirconia material (hereinafter referred to as "sintered PSZ material", when applicable.) This compression effect is essential in order to solve the problem that the ceramic transforms from the tetragonal into the monoclinic form.
The nozzle portion of the device is formed of a highly heat resistant ceramic material because of the severe temperature conditions found at that portion of the device. Affixing the nozzle portion to the surrounding metal member can also create problems. For instance, when the chamber liner is made of sintered PSZ material having a large thermal expansion coefficient and the nozzle portion is made of sintered Si.sub.3 N.sub.4 material, and both the chamber liner and the nozzle portion are covered with metal by the casting method, the contraction of the metal between the chamber liner and the nozzle portion is suppressed. As a result the compression effect is not sufficiently obtained on the sides of the sintered PSZ liner. Thus the design of the auxiliary chamber is limited.
FIG. 4 is a sectional diagram showing one example of a conventional auxiliary combustion chamber. In this auxiliary chamber, a disk-like nozzle piece 33, having orifice 37, is made of sintered Si.sub.3 N.sub.4 material. It is abutted against the open portion of a bell-shaped hollow chamber liner 32 of sintered PSZ material. The nozzle piece 33 and the chamber liner 32 are covered with a metal member 31 by the casting method previously described. In FIG. 4, the liner and the metal member have an injector nozzle insertion hole 35 and a glow plug insertion hole 36. In order to maximize the compression effect of the metal casting method, the hollow chamber liner is substantially bell-shaped, and the disk-like member performs satisfactorily as the nozzle of the auxiliary chamber.
In view of the foregoing, the present applicants have proposed "Heat Insulation Material for Auxiliary Chamber in Internal Combustion Engine" under Japanese Patent Application No. 135354/1983. This invention is intended to improve the invention thus proposed, and to solve the above-described problem accompanying such conventional devices and to fully utlize the ceramic characteristic of the auxiliary combustion chamber in an internal combustion engine.